dnsimple / dns_erlang / 14510773222

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Edns0 truncated record (#68)

The current implementation of erldns does not comply with RFC 6891 when handling truncated (TC) responses for EDNS0 queries. Specifically, the server fails to include an OPT record in truncated responses, which violates the requirements specified in Section 7 of RFC 6891. This could lead to compatibility issues with resolvers that expect standards-compliant behaviour, introducing additional latency due to retries or fallback to other name servers.

Additionally, erldns does not correctly handle unsupported EDNS versions — it should return an RCODE 16 (BADVERS) but currently responds with a valid (but non-compliant) response. Lastly, the infrastructure lacks NSID support, which could be useful for operational debugging.

Also ran successfully all these https://kb.isc.org/docs/edns-compatibility-dig-queries against erldns with this branch loaded.

* Implement correct EDNS0 truncation

* Ensure EDNS version is enforced

* Refactor encode_optrr to reduce code duplication

* Add linter to tests

* TODO: skip returning answers when BADVERS is set

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